1. Field of the Invention
The present invention relates to contactors for electronic parts and, more particularly, to a contactor for electronic parts that is used for a characteristic test of electronic parts such as a semiconductor integrated circuit device and a contact method using such a contactor.
2. Description of the Related Art
In recent years, miniaturization, reduction in thickness and reduction in weight of portable electronic equipments (telephones, cameras, personal computers, etc.) have been advanced, and improvement in performance, miniaturization and high-integration have also been advanced with respect to semiconductor integrated circuit devices (hereinafter, referred to as ICs) that constitute electronic circuits of such portable electronic equipments. In many cases, as a form of an IC package, a ball-grid array (BGA) type is used, which has a small pitch of terminals so as to save a space.
Moreover, in the fields such as a high-performance CPU or network equipments (a server or a switchboard), an operation at a higher speed is required. Thus, an attempt has been made to improve a processing speed by high-integration of internal circuits, which causes an increase in electric power consumption.
As a form of an IC package, many input and output electrodes and electrodes for power supply are required, and there is a demand for providing many electrodes in a limited space. Thus, a BGA type package having a larger number of pins is used in many cases.
ICs are subjected to a final inspection which is performed before shipment is in a manufacturing process of the ICs, and ICs judged as non-defective in the final inspection are delivered. In the final inspection, an IC tester is used for performing a characteristic test while supplying an electric power and electric signals from the IC tester so as to make judgment of good or bad of the ICs. A contactor such as an IC socket is used as an interface that connects an IC and the IC tester. The IC is connected to the IC tester through the contactor, and subsequently connected to electric testing circuits of the IC tester.
An example of a conventional contactor is shown in FIG. 1. FIG. 2 is an enlarged view of a part of the contactor shown in FIG. 1.
The contactor comprises a plurality of contact pieces 1 that contact with terminals of an IC. The contacts 1 are arranged in a base 2, and the base 2 is fixed to a substrate 3.
A cover 4 is arranged in the upper portion of the base 2. An opening that receives the IC is provided in the cover 4. By receiving the IC in the opening of the cover 4 and pressing the back surface of the IC, electrode terminals of the IC are brought into contact with the contact pieces 1, which achieves electric conduction.
As each contact piece 1, as shown, for example, in FIG. 2, a probe pin incorporating a coil spring is generally used. It should be noted that an illustration of the cover 4 is omitted in FIG. 2.
The contact pieces 1 are incorporated into the base 2 so that second contact portions 1b of the contact pieces 1 are brought into contact with terminals 3a of the substrate 3 in a continuously pressurized state.
The tests and measurements of the IC 5 are performed while achieving electric contact by causing electrode terminals 5a of the IC 5 to contact with first contact portions of the contact pieces 1 and pressing electrode terminals 5a to the contact pieces 1. Each contact piece 1 has a spring mechanism 1c including a coil spring so that an appropriate contact pressure is achieved by an elastic force of the spring mechanism 1c. 
FIG. 3 shows a part of another convention contactor. The conventional contactor shown in FIG. 3 does not have a spring mechanism such as a coil spring, and a contact pin 6 itself is a probe pin constituted by a bent spring. The contact pin 6 itself bends so as to be elastically deformable to achieve a contact pressure.
That is, an end 6b of the needle-like contact pin 6 is fixed to the substrate 3, and a contact portion is provided on the other end so that the contact pin 6 is elastically bent when the electrode terminal 5a of the IC 5 is brought into contact with the contact portion 6a and pressed against the contact portion 6a so as to achieve a contact pressure between the electrode terminal 5a and the contact portion 6a by an elastic returning force.
It should be noted that the end 6b of the contact pin 6 is inserted into a through hole provided in the substrate 3, and is electrically connected to a conductive layer in the through hole (not shown in the figure).
FIG. 4 shows another form of the conventional contactor. In the conventional contactor shown in FIG. 4, a guide plate 7 is elastically supported by a shaft 9 and a coil spring 8 fit on the shaft 9 on a base 2. The shaft 9 penetrates a guide plate 7 and is inserted into the base 2. According to this configuration and arrangement, the guide plate 7 is movable in a vertical direction (directions indicated by arrows in the figure) with respect to the base 2.
First contact parts 1a of contact pieces uprightly held on the base 2 are inserted into holes formed in the guide plate 7 and connected to electrode terminal guiding parts 90. Each of the holes has an inner diameter larger than an outer diameter of each of the first contact portions 1a of the contact pieces 1 as well as each of the electrode terminal guiding parts 90.
In the contactor having the above-mentioned structure, the electrical connection between the electrode terminals 5a of the IC 5 and the first contact portions 1a of the contact pieces 1 can be attained as follows.
First, an IC holding and pressing part 22, which holds the IC 5, is moved, so that the electrode terminals 5a of the IC 5 are positioned substantially above the electrode terminal guiding parts 90. Then, the hold of the IC 5 by the IC holding and pressing part 22 is cancelled and the IC 5 is fallen by gravity so as to cause the electrode terminals 5a of the IC 5 into the respective electrode terminal guiding parts 90.
The electrode terminals 5a of the IC 5 slide into the electrode terminal guiding parts 90 by gravity, and the electrode terminals 5a are brought into contact with the respective first contact parts 1a. 
Subsequently, the electrode terminals 5a press the first contact portions 1a of the contact pieces 1 by pressing the IC 5 by the holding and pressing part 22 or other pressing jigs. Consequently, an appropriate contact pressure is obtained according to the elastic forces of the coil springs 8 and spring mechanisms 1c incorporated in the contact pieces 1, and electric connection between the electrode terminals 5a of the IC 5 and the first contact portions 1a of the contact pieces 1 can be obtained.
In each case of the conventional contactors, a direction of deformation of the first contact portion 1a or the contact portion 6a is limited only to a direction substantially the same as the direction of being pressed (a vertical direction in the structure shown in the figures), and a deformation is permitted only a distance corresponding to tolerances of assembly with respect to directions (transverse directions or horizontal directions in the structure shown in the figures) different from the direction of being pressed.
With progress in improvement in performance and miniaturization of electronic parts such as the above-mentioned IC, a number of terminals is increased and a pitch between the terminals is decreased. Thereby, it has become difficult to bring all terminals of an IC into contact with corresponding contact pieces of a contactor with an appropriate positional relationship.
That is, if an attempt is made to arrange the contact pieces of the contactor at positions corresponding to the electrode terminals of the IC, each of the electrode terminals of the IC cannot agree with the corresponding one of the contact pieces since there is a positional error in the positions of the contact pieces and the there also is a positional error in the electrode terminals of the IC. Accordingly, it is difficult to obtain a good contact and there it may be difficult to perform a desired electric test.
Specifically, a large part of the electrode terminals contacts with contact portions of the corresponding contact pieces with low contact resistances, while a part of the electrode terminals is brought into contact with the contact portions of the contact pieces at positions off from the center thereof due to the positional errors of the electrode terminals of the IC and the contact pieces of the contactor, which causes a problem in that the contact is made in a state where only a low contact resistance is achieved.
Although the required position accuracy can be relaxed by increasing an area of the contact portions of the contactor, it is not practical to increase the area of the contact portions since further reduction has been progressed in the pitch of the electrode terminals of the IC.
Moreover, the contact portion of the probe pin type contactor shown in FIG. 2 and FIG. 3 moves only in a vertical direction (longitudinal direction) and hardly movable in a horizontal direction (transverse direction).
For this reason, even if the center of the electrode terminal of the IC and the center of the contact portion of the contact piece do not match each other, a contact must be made in such a state. It is considered that the contact pieces can be moved while accurately recognizing positions of the electrode terminals by image recognition, it is difficult to make positioning by moving each contact piece individually.
Moreover, in the structure shown in FIG. 4, if the weight of the IC 5 is small, there may be a case where the IC 5 stops in the middle of falling due to a friction between the IC 5 and the electrode terminal guiding parts 90 and does not fall to the end by gravity only. In such a case, if the IC 5 is forcibly pressed by the holding and pressing part 22 after the IC 5 is fallen by gravity, the electrode terminals 5a may be damaged due to the pressure to force the electrode terminals 5a to completely contact with the first contact portions 1a despite of misalignment between the electrode terminals 5a and the electrode terminal guiding parts 90 or the first contact portions 1a. 
Furthermore, when causing the IC 5 to fall by gravity, the IC 5 is released from the IC holding and pressing part 22 and is caused to fall so as to cause the electrode terminals 5a of the IC 5 to contact with the first contact portions 1a of the contact pieces 1 via the electrode terminal guiding parts 90, which requires a predetermined falling period. Such a falling period is a waste time, and may result in deterioration in work efficiency.
Moreover, in a case where a test measurement is carried out in a state in which not a chip individualized from a wafer but a plurality of devices (chips) are connected with each other such as in a wafer-level CSP (Chip Size Package) or a bump wafer, since the plurality of devices connected with each other are larger in size and heavier than a contactor, it is difficult for the structure shown in FIG. 4 to position the electrode terminals of the devices to the electrode terminal guiding parts 90 or the first contact portions 1a by moving the devices.
Furthermore, although there may be misalignment in the positions of the contact electrodes of the plurality of devices, each of the connected devices cannot be moved individually with respect to the first contact portions 1a of the contact pieces 1. Thus, according to the positioning to move the device side, there may be a case where one of the first contact portions 1a of the contact pieces 1 can be positioned accurately but misalignment cannot be avoided with the first contact portions 1a of other contact pieces 1. Accordingly, it is difficult to make an electrical contact by accurately positioning all of the electrode terminals of a plurality of devices to the first contact portions 1a of the contact pieces 1.
Moreover, with respect to a device having terminal surfaces of both sides or more, such as a POP (Package On Package), etc., since the device cannot be moved after once the contactor is positioned to electrode terminals on one side, electrode terminals on other sides of the device cannot be positioned accurately to other contacts.